A steering device mounted to a vehicle, such as an automobile, generally includes a steering shaft, which is supported by a steering column. Specifically, the steering shaft is connected at one end thereof to a steering wheel, and also connected at the other end thereof to a tire by means of an intermediate shaft or the like. In this circumstance, vibrations caused by rotations on an engine or a rough or bumpy load surface has been transmitted to the steering wheel by means of the steering shaft. To reduce the vibrations transmitted to the steering wheel as possible, the rigidity of the steering column has been enhanced.
A known steering device, disclosed in JP 2002-193110A, employs an electric tilt steering system and includes an electric tilt unit for tilting the steering column in a vertical direction, the steering column being connected to, for example, the vehicle steering wheel.
Such steering device further includes a column tube, the column tube being supported at a column tilting point so as to be tilted thereabout. Thus, when a driver operates a switch for adjusting the steering device, an angle of the steering column is adjusted by means of the electric tilt unit.
When the steering column is tilted, the column tube is slid in a vertical direction in a manner where a roughly triangular protruded shape of a sliding member of the column tube slides on a roughly triangular recessed shape of a contact portion (pressure pad) of the column tube. The contact portion is fastened to a housing, which is attached to the steering column, by means of a bolt so as to apply a pressure constantly to the column tube in a horizontal direction. Thus, by means of the bolt applying a pressure to the column tube, vibrations in a vertical direction or a horizontal direction of the steering column can be reduced.
In this configuration, even when a load is applied to the steering wheel in a vertical direction or a horizontal direction, vibrations in a vertical direction or a horizontal direction on the steering column can be reduced; as a result, rigidity of the steering column can be enhanced.
Specifically, according to the known steering device, when the pressure is applied in a right direction, because the pressure is also applied to the column tilting point, at which the steering column is tilted, or applied to the tilt unit, the vibrations on the steering column cannot be reduced adequately, as a result, the vibrations transmitted to the steering wheel cannot be reduced. Further, in this circumstance, load fluctuation may be easily generated, and rotations of the motor may become uneven, as a result, a level of the noise may be increased.
Further, because the column tube is fitted to the housing at the tilt unit side by means of a nut, and also fit to the housing at the contacting portion by the sliding member, when a large pressure is applied to the column tube at the steering wheel side in a vertical direction, the column tube may be disengaged from the sliding member so that the column tube may become unstable. Consequently, a rotational moment is applied to the fitting portion of the column tube at the tilt unit side; as a result, it becomes difficult to secure rigidity of the steering column.
Thus, a need exist for the steering device to improve rigidity of the steering column in order to reduce vibrations from transmitting to the steering wheel.